Even as it gains momentum and attracts substantial donations following a string of primary-election wins, the “tea party” movement is facing the challenges of a grass-roots organization that has no central leadership or single goal.

On Tuesday, word spread that Tea Party Nation had canceled for lack of interest the convention it planned to hold in Las Vegas next month. Some tea party activists have frowned upon the Tennessee-based group, which was accused of profiteering when it charged $500 for admission to its first convention, in Nashville, in the spring.

And Tea Party Patriots, a national group based in Atlanta, announced that it would distribute a $1 million donation to local groups to encourage conservatives to vote in November’s midterm elections. But group leaders wouldn’t say where the money came from, fueling the perception that the movement relies on monied business and political interests that aren’t as ideologically pure as its grass-roots supporters.

The tea party movement, a loose confederation of conservative activists who began organizing shortly after President Obama took office, is best known for its protests against what its members view as out-of-control spending. But the organization also includes national groups that have staged some of the demonstrations, donated money to political campaigns and organized other events.

Judson Phillips, the founder of Tea Party Nation, did not return e-mail and phone requests for an interview.

Several tea party organizers in Nevada said they did not encourage activists to attend the convention because of a view that Tea Party Nation is more profiteer than genuine grass-roots organizer. Critics assailed the group in the spring not only for the cost of admission to its first convention but also for paying its keynote speaker, Sarah Palin, a $100,000 fee.

Tea Party Nation originally scheduled its second convention for July, but Phillips canceled that event, saying that Las Vegas would be too hot and that activists would rather convene in the fall. But this time around, some activists in Nevada said they were unaware of the convention, leaving open questions about the breadth of Tea Party Nation’s organization.

“I didn’t even know that was going on,” said Lee Kennedy, 46, a casino executive in Carson City who recently founded a group called Faith, Family and Freedom. “Whoever was putting that together obviously didn’t get the word out, because I didn’t know about it.”

National coordinators for Tea Party Patriots, meanwhile, announced at a news conference in Washington on Tuesday that an entrepreneur who wished to remain anonymous had donated $1 million to the organization. The money will be distributed within the next two weeks on a competitive basis to local groups that apply.

Of the major national tea party groups, Tea Party Patriots most closely resembles a grass-roots organization. The nonprofit group does not run a political action committee and does not endorse candidates. At least 2,800 local groups are affiliated with it, but Tea Party Patriots does not tell them what to do or whom to vote for.

The $1 million, organizers said Tuesday, will be spent on promoting the group’s three “core principles”: fiscal responsibility, limited government and free market enterprise. The money will be used to motivate like-minded voters to go to the polls on Nov. 2, but it will not be used to advocate for particular candidates.